A Biomechanics Core will serve all four proposed Projects, operating from our institution's Orthopaedic Biomechanics Laboratory. Existing general capabilities are in place for macroscopic-level physical testing of musculoskeletal tissues and constructs, and for finite element stress analysis and digital image analysis. Additionally, special capabilities to support the proposed SCOR projects have been developed in nine areas: (1) For Project 1, a unique image measure of comminution fracture severity, based on absorbed impact energy inferred from inter-fragmentary free surface area; (2) For Projects 1, 2, and 3, voxel-based contact finite element (FE) analysis, which greatly improves the practicality of patient-specific cartilage stress analysis; (3) For Projects 2, 3, and 4, poroelastic constitutive behavior both in conventional prescribed-traction FE and in the new voxel-based FE contact formulation; (4) For Projects 1, 2, and 3, collaborative with our Department of Radiology, air-injection contrast multi-detector CT scans as a new vehicle for highly accurate measurement of local cartilage and subchondral plate thickness; (5) For Projects 2 and 3, also collaboratively with our Department of Radiology, a new technique for assessing cartilage water content from multi-sequenced T2-weighted MRI scans; (6) For Projects 2 and 3, unique software for screen-displacement-axis measurement of ankle motion, using pulsed DC electromagnetic motion tracking equipment; (7) For Project 3, a servo-hydraulically driven loading/motion applicator for cadaveric ankle studies, which allows simulating physiologic ankle plantar/dorsiflexion cycles; (8) For Project 3, custom-designed TekScan piezorestive sensors for transient intra-articular contact stress measurements in human ankles; and (9) For Project 4, a new laboratory system for in-vitro study of cartilage explant specimens loaded cyclically to physiologic stress levels, under operator-controlled combinations of axial compression and shear. These nine special capabilities were developed by investigators based in the proposed Biomechanics Core, who therefore are well positioned to support their applications to the research plans for the respective SCOR Projects.